1. Field of the Invention
The present invention relates to a novel light-sensitive lithographic printing plate prepared by using a light-sensitive polyester containing an o-quinonediazido group as a terminal group.
2. Description of the Prior Art
It is well known to use light-sensitive quinonediazides for the production of photo copies and photoresists and for lithographic printing plates. These systems adroitly utilize the property that the solubility of the light-sensitive layer becomes different, as a result of exposure, between the exposed areas and the unexposed areas and, when treated with a suitable solvent, the desired image area remains on a support while unnecessary areas are washed away from the support. Detailed descriptions of this are given in U.S. Pat. Nos. 3,046,121, 3,046,122 and 3,046,123. In these patents, the above-described compounds are applied to a light-sensitive lithographic printing plate as naphthalenediazoxide esters or acid amides. In addition to these compounds, many compounds of this type have been reported.
However, most compounds of this type are low molecular weight compounds. Therefore, when these compounds are used alone, crystallization occurs and, as a result, a good film cannot be formed and the mechanical strength of the resulting images is so weak that it is difficult to make many copies thereof. Accordingly, these compounds are often used together with an alkalisoluble resinous binder or are used as a reaction product with an alkali-soluble resinous substance.
This type of polymer compounds is described in U.S. Pat. No. 3,046,120, British Pat. No. 1,113,759 and U.S. Pat. application Ser. No. 684,636, filed Nov. 21, 1967, now abandoned. The compounds described in these specifications are based on polymers such as a phenol resin, an aminostyrene resin, etc. Also, U.S. Pat. No. 3,647,443 describes light-sensitive quinonediazides having an o-quinonediazido group at the terminal of a polyalkylene glycol. However, these compounds possess the defect that coated layers prepared using them are fragile and have a comparatively poor flexibility, although they possess good light sensitivity and provide a sufficient difference in solubility between the exposed areas and unexposed areas.